1. Field of the Invention
The present invention relates to improvements in a method for making nonwoven fabrics whose nonwoven shape is held in position by friction resistance and/or entanglement of the individual fibers, without using any special binder to hold the fibers together.
2. Description of the Prior Art
Among the methods employed in the past for making nonwoven fabrics of this kind is one in which fine spray liquid streams are sprayed onto a web through conical nozzles as disclosed in U.S. Pat. No. 2,862,251. In another technique, jets of fine columnar liquid streams are impelled onto a web through circular nozzles as disclosed in U.S. Pat. No. 3,485,706. However, in the former method which uses fine spray liquid streams, the dispersal of the force of the liquid stream is so large and the liquid stream collides with the web in such a fine spray that the force of impact is very small. Consequently, the individual fibers which form on the support do not arrange themselves very quickly and clearly in a shape corresponding to the numerous apertures in the supporter. That is, the rearranging efficiency or the patterning efficiency of the fibers and the speed at which the fibers entangle, as well as the strength of the entanglement, have both been insufficient. On the other hand, in the latter described method the dispersion of the liquid stream, which occurs in the first method, does not occur in the latter method. Furthermore, the impact force of the stream per unit area on the web is large, but the individual columnar liquid streams are so fine that they collide with the web in the form of little dots. Therefore, the absolute force of impact on the web is still small. Accordingly, the entangling efficiency, in which many fibers quickly entangle with each other, and the rearranging efficiency, or the quick rate at which the fibers rearrange with each other, are still unsatisfactory. Further, in the method of the columnar liquid stream, clear linear loci are described on the web surface by the relative motion of the above-mentioned circular nozzle and the web. Accordingly, another deficiency of this method has been that uneven streaks of fiber are formed on the web.
A need, therefore, continues to exist for a method by which an entangled mass of fibers can be quickly formed on a web in an even thickness.